1. Field of the Invention
The present invention relates to a sheet receiving/stacking device for receiving and stacking sheets in a sheet stacker, and to an image forming apparatus having this sheet receiving/stacking device.
2. Description of the Related Art
Sheet discharging/stacking devices incorporating binding devices, such as staplers, for use in a printer and other image forming apparatus, are well known. Also well known is the type of sheet discharging stacker provided on a side surface of the printer near the discharge opening of the printer body and adapted to bind printed sheets corresponding to each job and to then discharge and stack the bound sheets.
The image forming apparatus is, for example, a copier, a printer, a facsimile machine, or a composite apparatus thereof. Furthermore, the sheet is, for example, a plain paper sheet, a thin resin sheet which serves as a substitute for the plain paper sheet, a postcard, a cardboard sheet, a letter sheet, and a thin plastic plate.
Usually, printers discharge sheets, printed side up. To receive and stack printed sheets in proper page order and to then bind such stacked sheets, the sheet discharging stacker of this type has a sheet reversing mechanism for reversing sheets so that the sheets each having the printed side face down are stacked in the page order, binding devices for stacking the printed sheets corresponding to each job and for aligning and binding the stacked sheets, and a discharging portion for stacking bundles of the bound sheets.
Therefore, a large space was required for installation of this conventional sheet discharging stacker. Moreover, the intervals between times at which receiving sheets are discharged from the printer body should be sufficient to allow for reversal of each of the sheets. Consequently, the ability of the printer to process sheets is reduced. Furthermore, the ability of the raw sheet discharging stacker to discharge and process sheets is reduced.
As a sheet discharging stacker for enhancing the ability of the printer to process sheets, there is known a "floor-standing type sheet discharging stacker", which has a sheet stacking device provided under the printer body and a conveying portion, provided outside the printer body, for causing sheets to go around and under the printer body.
This sheet discharging stacker conveys the sheets each having the printed face up along a longitudinal conveying path provided on the rear surface of the printer body. Then, the longitudinal conveying path reverses each of the sheets. Thus, the reversing mechanism becomes unnecessary. This eliminates the reduction in the ability to process sheets, which is caused by the reversing mechanism. Consequently, this sheet discharging stacker efficiently discharges sheets.
Furthermore, a conventional ordinary sheet discharging stacker has an aligning device for aligning printed sheets. This aligning device has an aligning portion that is inclined at about 10 to 30 degrees to the horizontal. The sheets are aligned by being made to abut against a longitudinal wall portion provided at an inclined end portion of the aligning device by utilization of the inclination of this sheet aligning portion and the weight of the sheets themselves. However, the provision of the aforementioned aligning device results in an increase in the height of the sheet discharging stacker. Moreover, when the sheet discharging stacker is provided under the printer body, the height of the entire printer is increased. This sometimes degrades the operability of the printer to users.
As a countermeasure against this, applicants of the instant application have devised a low profile technical feature that comprises a stacking tray serving as a sheet stacking device for stacking printed sheets, which is nearly horizontal by being inclined less than 10 degrees to the horizontal so as not to depend on alignment of sheets by their own weight. This technical feature further comprises a shutter serving as a sheet abutment device, which is provided in the stacking tray on a downstream side of a sheet conveying direction, a conveying belt serving as a conveying direction alignment device for pressing a sheet against the shutter, and alignment device, provided in a width direction thereof, for aligning the sheets. Thus, the size of the sheet discharging stacker is reduced by decreasing the height of the stacking tray as much as possible. Moreover, the height of the entire printer is reduced. Consequently, users can easily operate the printer.
The aforementioned sheet discharging stacker, however, has a drawback in that jamming occurs due to the fact that a face of a sheet previously brought into and stacked in the sheet stacking device catches a leading edge portion of a sheet later brought thereinto when sheets printed in the printer body are made to go around and are brought into the sheet stacking device nearly horizontally from the sheet conveying portion provided on the rear surface of the printer body.
As a countermeasure, there is proposed a sheet carrying guide disposed at a downstream end of a longitudinal conveying path provided in the vicinity of the sheet stacking device. However, when this countermeasure is taken, the sheet carrying guide is a hindrance to the alignment of sheets stacked in the sheet stacking device. Thus, sheets are sometimes not smoothly brought into the sheet stacking device.
Additionally, sheet jams occur in the image forming apparatus having the aforementioned sheet discharging stacker and hinders the smooth discharging of sheets.